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Monsoon depression amplification by moist barotropic instability in a vertically sheared environment

Journal Article · · Quarterly Journal of the Royal Meteorological Society
DOI:https://doi.org/10.1002/qj.3585· OSTI ID:1574333
 [1];  [2]
  1. Univ. of California, Berkeley, CA (United States)
  2. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
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Our report makes the case that monsoon depressions over South Asia can form from a variant of moist barotropic instability. Along with an idealized numerical framework in which the atmosphere is partitioned into a basic state and a perturbation, we simulate vortices resembling monsoon depressions that draw energy from the meridional shear of the monsoon trough and amplify when they interact with precipitating ascent. The influence of the basic state vertical shear on the vortex induces upward velocity, which couples precipitation with a Rossby-wave-like mode arising from dry barotropic growth, allowing the vortex to intensify. Sensitivity experiments reveal that both the sheared basic state and latent heating are necessary to achieve positive growth rates and that this process requires a sufficiently large initial perturbation. Trajectory analyses suggest that the combined flow of the vortex and the large-scale monsoon transport diabatically generated potential vorticity from southwest of the vortex into the vortex center, thus enabling growth. In contrast with tropical cyclones, this mechanism does not require a feedback between surface wind speed and surface heat and moisture fluxes, though this feedback does ultimately result in a slightly stronger vortex.
Research Organization:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Organization:
National Science Foundation (NSF); USDOE; USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Grant/Contract Number:
AC02-05CH11231; SC0019367
OSTI ID:
1574333
Alternate ID(s):
OSTI ID: 1543184
Journal Information:
Quarterly Journal of the Royal Meteorological Society, Journal Name: Quarterly Journal of the Royal Meteorological Society Journal Issue: 723 Vol. 145; ISSN 0035-9009
Publisher:
Royal Meteorological SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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Figures / Tables (13)

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Related Subjects

54 ENVIRONMENTAL SCIENCES
Indian Monsoon
barotropic instability
idealized numerical modeling
monsoon depression
monsoon low‐pressure system